Clinton’s campaign manager, Robby Mook, said on Sunday that “experts are telling us that Russian state actors broke into the DNC, stole these emails, [and are] releasing these emails for the purpose of helping Donald Trump”.

Leaked DNC emails reveal details of anti-Sanders sentiment

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“I don’t think it’s coincidental that these emails are being released on the eve of our convention here,” he told CNN’s State of the Union, alluding to the party’s four-day exercise in unification which is set to take place this week in Philadelphia.

Robby Mook listens with other aides as Hillary Clinton speaks in New Hampshire earlier this month. Photograph: Brian Snyder/Reuters

Emails released by Wikileaks on Friday showed members of the DNC trading ideas for how to undercut the campaign of Senator Bernie Sanders, who proved a resilient adversary to Clinton in the Democratic primary. In one email, a staffersuggested the DNC spread a negative article about Sanders’ supporters; in another, the DNC’s chief financial officer suggested that questions about Sanders’ faith could undermine his candidacy.

“I think I read he is an atheist,” the staffer wrote. “This could make several points difference with my peeps. My Southern Baptist peeps would draw a big difference between a Jew and an atheist.”

Wikileaks, which did not disclose how it acquired the emails, has promised more releases. Earlier this year, the DNC and an independent cybersecurity firm said the party’s email system had been breached by Russian hackers, though a hacker by the moniker “Guccifer 2.0” has also claimed to have stolen emails.

In June Florida congresswoman Debbie Wasserman Schultz, the DNC chair, said the breach was a “serious incident” and that the cybersecurity firm had “moved as quickly as possible to kick out the intruders and secure our network”.

Late on Saturday, the DNC announced that Wasserman Schultz had been removed from the convention program, according to CNN.

The DNC’s chief financial officer, Brad Marshall, apologized on Saturday for his remarks in the released emails, writing on Facebook: “I deeply regret that my insensitive, emotional emails would cause embarrassment to the DNC, the chairwoman, and all of the staffers who worked hard to make the primary a fair and open process.”

A day earlier he had told the Intercept: “I do not recall this. I can say it would not have been Sanders. It would probably be about a surrogate.”

Also speaking to CNN on Sunday, Sanders said he found the emails “outrageous”, but said they were “not a great shock to me”.

He said: “I mean, there’s no question to my mind, no question to any objective observer’s mind, the DNC was supporting Hillary Clinton and I’m not shocked by this.”

“I don’t think she is qualified to be the chair of the DNC,” he said, “not just because of these emails, which revealed the prejudice of the DNC, but also because we need a party that reaches out to working people and young people. And I don’t think her leadership style does that.”

But the senator, who endorsed Clinton last month, declined to focus his anger towards her, saving it for Trump. Sanders said he was proud of the concessions his campaign had won from Clinton on the Democratic platform, and praised her vice-presidential pick, Tim Kaine, as “an extremely bright guy, an extremely nice guy”.

“What is most important is defeating the worst candidate for president that I have seen in my lifetime,” he said. “I can’t speak for 13 million people, but I think most of my supporters understand Trump has got to be defeated; we need to elect as many progressives as possible.”

The senator will speak at the convention on Monday night, and his team released a preview that said he would not only attack Trump but speak about the future of the “political revolution” that he promised on the campaign trail. “Our campaign was about revitalizing American democracy. I want to see that incorporated into the Democratic platform.”

The Russian president, Vladimir Putin, has claimed Russia does not meddle in other countries’ domestic affairs, despite overwhelming evidence and the Kremlin’s admission that it has helped rebels in eastern Ukraine. Putin has insisted he could work with Clinton or Trump. Russian, Chinese and American intelligence agencies frequently blame each other for hacking attacks as part and parcel of their status as competing countries, though the substance of those hacks are rarely dumped into the public domain.

Trump’s campaign has indirectly fuelled speculation that the Kremlin would prefer the businessman to Clinton as the next president. His campaign stripped hawkish language from the Republican party’s official stance toward Russia, removing a proposal to give weapons to Ukraine in its continuing struggle with pro-Russia separatists. The head of Trump’s campaign, Paul Manafort, was formerly on the payroll of Ukrainian president Viktor Yanukovych, who was ousted twice for his attempts to draw the country closer to the Kremlin.

At rallies, he has repeatedly asked: “Wouldn’t it be nice if we could get along with Russia?”

On Sunday, the Trump campaign rejected Mook’s allegations, Manafort telling ABC’s This Week they were “absurd” and “pure obfuscation on the part of the Clinton campaign”.

“What those emails show is that it was a clearly rigged system, and that Bernie Sanders never had a chance,” he said.

His son, Donald Trump Jr, appeared on CNN’s State of the Union. “They should be ashamed of themselves,” he said of the Clinton campaign. “If we did that … if my father did that, they’d have people calling for the electric chair. It just goes to show you their exact moral compass. They’ll say anything to win this.”

Trump himself used Twitter to pass comment, saying: “Sorry folks, but Bernie Sanders is exhausted, just can’t go on any longer. He is trying to dismiss the new emails and DNC disrespect. Sad!”